Method of gas plating an alloy of aluminum and magnesium



May 2, 1961 F. E. DRUMMOND 2,982,016

METHOD OF GAS PLATING AN ALLOY 0F ALUMINUM AND MAGNESIUM Original Filed April 1 2, 1955 fig- 1 COMPOSITE METAL SHEET LIGHT METAL SHELL ALUMINUM OR MAGNESIUM LIGHT METAL INTERLOCKED WITH BASE METAL STEEL, IRON, COPPER, ETC.

COMPOSITE METAL CABLE INVENTOR E. DRUMMOND ATTORNEY METHOD or GAS PLATING AN ALLOY on AND MAGNESIUM Folsom E. Drummond, Washington, D.C., assignor, by

mesne assignments, to Union Carbide Corporation, New York, N.Y., a corporation of New York 3 Claims. (Cl. 29197) This invention relates to methods of gas plating light metals of groups II and III of the periodic table of ele ments, and particularly magnesium, aluminum, beryllium, zinc, cadmium, scandium, gallium, indium and the like, on metal surfaces to form composite metal bodies.

This application is a division of application Serial No. 500,978, filed on April 12, 1955, and is now Patent No. 2,876,137.

While the invention will be described more particularly with respect to gas plating aluminum and magnesium, it will be understood that this invention also is applicable to the other metals of the aforementioned groups.

It has been attempted heretofore to form composite articles of various metals and light metals such as magnesium and aluminum, but it has not beensuccessful without the use of intermediate bonding layers. This has been resorted to because of the weak bond produced benited States Patent to a supporting base metal without the necessity of employing an intermediate bonding layer or alloy as hasbeen the practice heretofore.

Another object of the invention is to provide an im proved method of gaseous metal plating these light metals of group II and IIl of the periodic'system onto the surfaces of articles by gaseous metal plating.

It is still another object of the inventionto provide a method for producing aluminum coated articles whereby aluminum metal is deposited onto the surface of the substratum and into the pores and interstices of the surface to provide an interlocked substantially integral layer 'or coating of aluminum metal thereon. v v

These and other objects and advantages will become; apparent as the description proceeds.

In accordance with the present invention, metal surfaces such as magnesium, aluminum, steel, iron,--copper.

tween these light metals and the metal surfaces on which they are applied. This is due largely to their great affinity for oxygen. The'present invention is designed to overcome these difficulties for all practical purposes, and provide a method of plating these light metals onto different metal surfaces.

In accordance with the present invention, aluminum or magnesium metal, or suitable mixtures thereof are deposited directly -upon a substratum which may be composed of metals such assteel, iron, copper, magnesium, aluminum, or metal alloys to provide a tenaciously bonded metal layer or coating'of light metal. The process thus avoids the necessity of utilizing an intermediate bonding layer as has heretofore been the practice.

The principal object of the present invention is'to apply a light metal such as aluminum or magnesium directly onto a base metal including aluminum and magne sium and alloys thereof, whereby the same is provided with an outer shell or portion formed substantially of pure aluminum or magnesium.

Another object of the-invention is to provide a composite metal article consisting of substratum of light metal and an outer coating or layer of aluminum metal.

Another object of the invention is to provide a composite metal article of the character described, which comprises a gas plated layer of aluminum metal or magnesium metal. I

Another object of the invention is to provide a method whereby light metal, such as magnesium and aluminum,

may be plated onto metal castings, sheets, strips or the i and the like, and alloy metals are cleaned to remove for eign matter and then subjected-to gas plating utilizing a suitable heat-decomposable organometallic compound of aluminum, magnesium, boron, beryllium, or suitable alloy-j or mixtures thereof, to provide a finished composite metal product. Alkyl metal compounds of these lightmetals are used as gaseous thermally decomposable com-- pounds which in contact with the heated substrate decompose and deposit an adherent protectivefilrn onto the substrate. 1 The following examples are illustrative of how the in vention may be practiced but are not intended to be restrictive of the invention.

Example I '4 Magnesium metal casting sand blasted to provide a clean surface is heated to about 350 C.4 00 C. in an atmosphere of dry helium containing magnesium diphenyl. This magnesium orga'nometallic compound decomposes at about 280 C. disassociating into magne sium and diphenyl. The process is carried out under atmospheric pressure conditions and in the absence of moisture to avoid fire hazard. In this instance the deposition of magnesium may be according to the equation- Example II Magnesium sheet metal is gas plated with magnesium metal similarly as in Example I, but under sub-atmos' pheric pressure conditions of from 1825" mercury, and using dry nitrogen as the inert gas carrier for magnesiumdiphenyl.

' Example 111 Iron castings are gas plated with magnesium as in Example III employing methylmagnesium iodide whichthermally decomposes at about 250 C.

Example V Magnesium metal is gas plated on steel as. in Example Ill using triarylmethylmagnesium iodide and .at--plat-' ing temperatures to bring about thermal decomposition of the iodide in an atmosphere of dry inert gas, e.g., nitrogen;

Example VI In this instance a 50-50 weight mixture of aluminum Patented MayZ, 196 1 Example VII Copper plate is cleaned and heated in an atmosphere of helium at a temperature of about 385 C. and in which is introduced approximately 10% of aluminum trimethyl. This compound boils at about 135 C. and is caused to disassociate to deposit the metal.

Example VIII Boron protective films may be deposited employing alkyl borate vapor, e.g. ethyl borate (C H is vaporious at 100 C.

Example IX Beryllium protecting films may be deposited using beryllium di-ethyl which is vaporous at 190 C.

These different light metals are thus gas plated directely onto a substrate metal which may be an alloy metal such as steel, copper, iron, or the like whereby there is produced a composite product comprising the light metal integrally and tenaciously bonded to the metal substrate.

Other organometallic compounds which may be used to gas plate these light metals, as described, are magnesium dimethyl; aluminum trimethyl; triarylmethylmagnesium halides; dipheny-lethynylmagnesium, aluminum hydride magnesium and aluminum nitrides, and/or mixtures of these metal compounds, and such as will thermally decompose under the temperature, pressure and inert atmosphere conditions imposed. The light metal halide compounds such as bromides, iodides or chlorides may be obtained from sea water or formed as by-products during the recovery or process of making various chemical compounds and products utilizing brine-containing waters.

Gas plated coatings of these light metals may be deposited to various thickness, as desired, depending upon the use to which the article is to be put. A coating of 0.001 .to 0.0025 inch is generally adequate for securing protection against corrosion in most instances.

The process makes possible continuous straight line production of composite heavy and light metal products, for example wire, cable, metal plate, strip, sheet material or screen.

.-A composite metal product made of a base metal gas plated with a light metal such as aluminum or magnesium is illustrated in the drawings:

Fig. 1 illustrates a composite metal sheet;

Fig. 2 is an enlarged fragmentary view in cross-section; and

Fig. 3 illustrates a composite metal cable.

The thickness of the coating may be controlled by limiting the duration of the gas plating or time the article remains in the plating enclosure. The invention is particularly useful in aluminizing metals where it is desirous that the metal be deposited penetrates the pores and interstices to form a substantially integral outer shell of aluminum metal.

The material being gas plated with the light metals may be composed of various metals or alloys and in the various shapes and forms described. To clean the metal preparatory to gas plating, use may be made of conventional methods, such as washing or immersing the material in alkali or acid solutions, and rinsing with clear hot water and heating to 150 to 200 C. for sufl'icient time to drive off all moisture and produce a perfectly dry surface. Electro-chemical cleaning methods as commonly used also may be employed if desired as well as mechanical cleaning methods, eg wire brushing and sandblasting.

Preheating and drying of the article prior to gas plating is preferably carried out in an inert atmosphere such as nitrogen, helium or the like to prevent oxidation. Thereafter the heated and completely dry metal surface is subjected to gas plating.

By employing gas plating in accordance with this invention, it is possible to envelope the material or article by a metal film or plate of any desired thickness, and which consists of substantially pure metal. A protective film is thus provided which film or plating does not have occluded foreign matter such as undesirable metals, salts, anode particles, bubbles and the like, which are inevitably plated out on the cathode along with the desired metal during ordinary electroplating methods. Oxygen and oxidizable materials are also absent. The plating deposited by such gas plating method has been observed to produce a metal deposit which penetrates into the V pores and interstices of the substrate metal but does not produce the undesirable brittle alloy effects as observed when such plating is applied by wet processes or molten metal plating methods. It is not known the exact reason for this, but it is believed that these beneficial effects are accounted for by reason of the freedom of the metal deposit from impurities, particularly metal impurities which produce the brittle alloy characteristic property. The metal deposit at the interstices of the substratum by gas plating produces a tenacious intermediate portion which remains ductile and tough so that the metal thus plated can be worked as desired. Any desired thickness of plating may be deposited by gas plating, for example, so thin that the metal area is actually transparent and when deposited on a transparent substratum, such as glass, produces a smoked glass. The metal plating may also be increased so as to provide a coating thickness such as /1 to A if desired, or greater.

In the use of conduit, pipe and the like conveying corrosive material, it is desirable to coat or plate the interior of the pipe so that it will resist corrosion. This may be done by gas plating so that the inner wall is resistant to corrosion. Metal plating done in this manner is very superior to wet plating methods because it has been difficult to bring about uniform plating on the interior of hollow objects, especially conduits. Furthermore, employing conventional wet electroplating methods there is always a certain amount, even though minor, of entrapment of electrolyte. While this may be imperceptible under ideal conditions, there is generally enough impurities plated out with the metal to ultimately cause deterioration of the plated article. Gas plating eliminates these difiiculties because no electrolyte is present or required in order to carry out the process and as is a prerequisite element in performing the wet electrolytic plating process.

Further, gas plating makes it possible to bring nascent pure metal in direct contact with chemically clean substrate surfaces on which the metal is to be plated, and due to the deposition of the metal from a gaseous state, the penetration of the same deeply into the pores and interstices of the metal is accomplished without the inclusion of impurities and such as will alter the physical characteristics of the metal so that the interstitial plate portions function to actually enhance the physical characteristics of the base metal or substrate.

While the preferred procedure and a number of examples are given illustrating embodiments of the invention, and how the same could be carried out, it is to be clearly understood that this application is not to be restricted thereto, and that various changes and modifications as may occur to those skilled in the art may be made without departing from the spirit and scope of the invention, and as more particularly set forth in the appended claims.

What is claimed is:

1. A method of providing a metal body with an outer shell or layer of aluminum and magnesium metal which ous mixture composed of the metal alkyls aluminum triethyl and magnesium diethyl, and maintaining the temperature high enough to cause decomposition of the aluminum and magnesium alkyls and deposition of aluminum metal and magnesium metal onto said metal body and into the pores and interstices thereof.

2. A composite metal product produced in accordance with the process of claim 1.

3. A method of providing a metal body with an outer shell or layer of aluminum and magnesium metal which comprises the steps of cleaning the metal body in a dry,

' inert atmosphere and thereafter subjecting said heated metal body while retained in said atmosphere to a gaseous mixture composed of a 1:1 weight mixture of aluminum triethyl and magnesium diethyl, and maintaining the temperature of said metal body high enough to cause decomposition of said gaseous mixture and deposition of aluminum metal and magnesium metal onto said metal body and into the pores and interstices thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,770,177 Martin July 8, 1930 2,619,433 Davis et a1. Nov. 25, 1952 2,804,397 Goodman Aug. 27, 1957 2,847,320 Bullofl Aug. 12, 1958 2,876,137 Drummond Mar. 3, 1959 

1. A METHOD OF PROVIDING A METAL BODY WITH AN OUTER SHELL OR LAYER OF ALUMINUM AND MAGNESIUM METAL WHICH COMPRISES THE STEPS OF CLEANING THE SURFACE OF THE METAL BODY, HEATING THE RESULTANT CLEANED METAL BODY IN A DRY, INERT ATMOSPHERE AND THEREAFTER SUBJECTING SAID HEATED METAL BODY WHILE RETAINED IN SAID ATMOSPHERE TO A GASEOUS MIXTURE COMPOSED OF THE METAL ALKYLS ALUMINUM TRIETHYL AND MAGNESIUM DIETHYL, AND MAINTAINING THE TEMPERATURE HIGH ENOUGH TO CAUSE DECOMPOSITION OF THE ALUMINUM AND MAGNESIUM ALKYLS AND DEPOSITION OF ALUMINUM METAL AND MAGNESIUM METAL ONTO SAID METAL BODY AND INTO THE PORES AND INTERSTICES THEREOF. 